A category of electronic cards concerned by the invention is made up by cards without exterior electrical contact and possessing a coil enabling electromagnetic coupling with an external arrangement.
By card is understood every object having a substantially planar structure defining a general plane of the object and exhibiting any contour whatsoever in such general plane.
The patent document EP 0 570 784 in the name of the present applicant describes various embodiments of an electronic card comprising a layer formed by a solidified binder in which is incorporated at least one electronic element electrically coupled to a coil. This document also describes various embodiments of a method of manufacture of such a card.
In a particularly advantageous embodiment, there is provided a positioning structure exhibiting at least one principal opening in which is housed the electronic element. In each embodiment described, the coil and the electronic element are housed within such principal opening. In all the proposed embodiments, the various elements incorporated within the solidified layer of binder are located facing entirely planar surfaces.
According to an embodiment of the method of manufacture described in the patent document EP 0 570 784, the following various steps for the manufacture of a card are provided:
I) the bringing onto a work surface of a first outer layer formed from a solid material;
II) the placing of at least one electronic element on the first outer layer;
III) the bringing of a binder onto the first outer layer;
IV) the bringing onto said binder of a second outer layer formed from a solid material and facing the first outer layer;
V) the application of a pressure on the first and second outer layers until such outer layers are located at a predetermined distance relative to one another.
In a final step, the binder is solidified in order to form an intermediate layer between the outer layers.
According to a specific characteristic of the method described hereinbefore, a positioning structure, defining at least one internal zone serving in particular for positioning the coil, is brought in between steps I and IV of the method.
According to a variant of the method described hereinbefore, it is foreseen to bring initially the planar outer layer and the various elements to be incorporated into the card, in particular the electronic element electrically coupled to the coil and also a positioning structure when the latter is provided. Next, the binder is applied in the form of a viscous liquid. Onto such binder is then applied the second outer layer. Finally, with the help of pressing means, pressure is exerted on the outer layers and consequently on the binder along a direction perpendicular to the work surface so as to form the layer of binder in which are incorporated various elements as provided.
The variant of the method described hereinbefore is very advantageous from an economic viewpoint since it enables producing large quantities of cards at low cost. Additionally, such variant is advantageous from the fact that it does not necessitate applying heat in order to melt the outer layers, thus avoiding the shrinkage phenomena of the material and buckling of the card once cooled. However, the applicant has observed in the course of numerous experiments that the method described hereinbefore brings results which are satisfactory for various specific embodiments, but that on the other hand a certain number of cards obtained by this method and having one of the structures proposed in patent document EP 0 570 784 does not exhibit a sufficiently satisfactory flatness such that for certain embodiments the industrial yield is relatively low.
Effectively, the requirement of flatness for electronic cards is particularly high, in particular when printing is provided on an external surface of such cards. Certain printing techniques require absolutely planar outer surfaces, lacking which deformations appear in the printed message.